1. Field of the Invention
The present invention relates to a control device for writing data into a display frame memory which is applied to simultaneous displaying of a plurality of pictures on a display surface of a computer system, or multi-window display.
2. Description of the Prior Art
FIGS. 4 and 5 illustrate hardware structure of the prior art display control devices for computer systems, wherein FIG. 4 is a block diagram showing an example employing a display controller. In the case of this structure, during a display cycle when some data on a display frame memory 1 is displayed on a desired display surface, a display controller 10 sends addresses for successive displays to the display frame memory 1 and the data to be displayed are loaded from the display frame memory 1 into a shift register 2 so as to be shifted thereby according to a display dot clock and output therefrom as video signals. And, during a write cycle when the data are written into the display frame memory 1, the display controller 10 sends the addresses where the data should be written in the display frame memory 1 and takes in the data once through an output control buffer 3, and, after processing the same in a predetermined manner, writes the same into the display frame memory 1.
FIG. 5 is a block diagram showing an example where a CPU 20 makes direct writing by the use of a display timing generator 4. In this case, during the display cycle, the display timing generator 4 sends addresses for displays to the display frame memory 1 in succession through an address multiplexer 5, and the data to be displayed are loaded from the display frame memory 1 into the shift register 2 so as to be shifted thereby according to a display dot clock and output therefrom as video signals. During the write cycle, the CPU 20 sends the addresses where the data should be written to the display frame memory 1 through the address multiplexer 5 and takes in the data once through the output control buffer 3, and, after processing the same in a predetermined manner, writes the same into the display frame memory 1.
In the prior art systems as respectively indicated in FIGS. 4 and 5, the processes for verifying addresses of windows in the multi-window displaying were all performed by means of software. Such software was complex so that the rate of processing speed was lowered.